The condensation reaction of saturated carboxylic acids and esters with carbonyl compounds to produce unsaturated acids and esters is known in the art. U.S. Pat. No. 2,734,074 discloses that formaldehyde reacts with lower alkyl esters of aliphatic monocarboxylic acid to produce lower alkyl esters of alpha-beta unsaturated acids in the presence of a dehydration catalyst. Suitable catalysts found in this reference are lead chromate on silica gel, zinc chromite on silica gel, vanadia on alumina, zirconia on silica gel, or lead sulfate on silica gel.
U.S. Pat. No. 3,014,958 discloses an improvement upon this reaction by having present, in the reaction mixture, a substantial concentration of the desired unsaturated ester, generally exceeding about 7% of the weight of reactant ester. The reaction is again performed in the presence of a dehydration catalyst, suitable catalysts being phosphates of alkali and alkaline earths, aluminum and boron. Additionally, oxides, including mixed oxides of 20 additional metals are disclosed such as zinc, vanadium, chromium, molybdenum, tungsten, etc.
U.S. Pat. No. 4,165,438 discloses that acrylic acids and esters are produced by reacting a lower alkanoic acid or lower alkyl ester with formaldehyde in the presence of a vanadium orthophosphate catalyst having a specific surface area. For comparison purposes, this reference discloses inferior phosphate catalysts of lithium, sodium, magnesium, zinc, aluminum, chromium, cerium, niobium, antimony and bismuth.
Other catalysts useful in this reaction have been supported rare earth metal oxides disclosed in U.S. Pat. No. 3,701,798; X or Y zeolites with cesium, rubidium or potassium cations as found in U.S. Pat. No. 4,115,424; pyrogenic silica promoted with Groups IIA and IIIA metals disclosed in U.S. Pat. No. 3,933,888; and phosphates of magnesium, calcium, aluminum, zirconium, thorium or titanium as found in German Pat. No. 2,615,887.